The present invention relates to an arrangement for cooling the piston of a rotary piston internal combustion engine that includes a housing which has a central portion with a trochoidal liner surface in the form of a double arc of a circle, and also has two side portions; a eccentric shaft passes through the housing at right angles thereto, and has an eccentric on which rotates, at a speed ratio of 2:3 relative to the rotation of the shaft, a triangular piston that is cooled by a mixture of fuel and air that flows therethrough.
An engine of this type is described in DE-OS No. 25 53 47, FIG. 7 (DE-P No. 25 60 063), where a partial stream of the fuel and air mixture is conveyed through the piston to cool the latter, and is conveyed via a channel in one or both side walls into side inlets. This partial stream is a rich mixture, so that due to the evaporation of the fuel contained therein on the hot inner walls of the piston, a better cooling effect, and at the same a preparation of the fuel, is achieved. The fuel is supplied to the air for combustion via a carburetor. The introduction of the intake air, or of the fuel and air mixture, into the piston for the purpose of cooling the latter was already mentioned in DE-AS No. 1 136 532.
However, especially at higher engine loads, such an air or mixture cooling of the piston is unsatisfactory and cannot cool the particularly thermally stressed parts any more than the less stressed parts.
The heat distribution on the piston results from the spreading of the flame in the direction of rotation; consequently, the highest temperatures occur at the center of the leading part of the respective piston side and near the leading piston corner, whereas the trailing part of the piston side remains relatively cool. The temperatures at full load, which reach up to 500.degree. C., result in the carbonization of oil (formation of carbon deposits) that calls in question a lubrication of the sealing elements and cakes the latter in their grooves. This results in leakiness of the working chambers, high wear, and failure of the engine. It is customarily attempted to reduce the temperatures by appropriate guidance of air within the piston, and by additional cooling ribs on the housing. However, the problem always produces transfer of heat in the direction toward the piston bearing, so that cooling of the housing is ineffective. On the other hand, internal cooling of the piston with gas as such can be increased considerably even during a preferred directing of the gas stream against the hot corner regions.
It is an object of the present invention, with the aforementioned type of engines, to achieve an additional effective cooling of the piston in the region of the high-temperature-stressed leading part of the piston side, and to thereby make such engines having air or mixture cooled pistons also usable for high loads, as is possible with such engines that have liquid-cooled pistons. A further object of the present invention is to bring about, with the same features, an effective preparation of the fuel already prior to introduction of the fuel and air mixture into the working chamber.